The present invention is especially related to improved feeding mechanisms for trim presses of the general type shown in U.S. Pat. Nos. 4,173,161 and a commonly owned copending application Ser. No. 06/145,899, filed May 2, 1980, now U.S. Pat. No. 4,306,474, which are incorporated herein by reference. These types of presses are employed to trim or sever articles from a sheet of thermoplastic material in which the articles have been integrally formed, generally in uniformly spaced rows. The trimming operation is performed by a cyclically reciprocated die and the feeding mechanism of the machine is operable to feed the sheet with the integrally formed articles to the die in step-by-step movement synchronized with the die reciprocation. Such sheets are usually formed with uniformly spaced projecting feed tabs which are engaged by the reciprocating feed fingers of the feed mechanism to advance the sheet one step toward the die on each feeding stroke of the feeding fingers.
Because the feed fingers must be located somewhat upstream of the feed path from the die assembly, accurate trimming of the articles from the sheet by the die is dependent upon precisely locating the end limit of the feeding stroke of the feed fingers relative to the die so that, at the conclusion of a feeding stroke, the row of articles to be trimmed is precisely aligned with the die.
While presently commercially available feed mechanisms are conventionally provided with adjustable elements to vary the location of the end of the feeding stroke of the feed fingers relative to the die, these adjustments almost invariably are of a nature such that it is necessary to make the adjustments while the various parts of the machine are stationary. This frequently requires a time-consuming trial and error process in which an initial adjustment is made, the machine is placed in operation, then shut down and readjusted, and the cycle repeated until inspection of the trimmed parts shows that alignment has been achieved.
Because the prior art mechanisms conventionally employ a substantial number of reciprocating and oscillating parts, a practical upper limit on the production rate of such machines is imposed. Each reciprocating or oscillating part must cyclically reverse direction which requires that the part be decelerated as it approaches one end of the stroke and then accelerated as it leaves the point of stroke reversal. The impact type loading imposed by such stroke reversals increases rapidly as the frequency of reversal increases, forcing the machine designer to compromise between a desired production rate and a desired degree of rigidity of the individual parts of the machine.
The present invention is especially directed to a solution of these two latter problems, and provides a machine in which the feeding stroke may be precisely located relative to the die while the machine is in operation, and by an arrangement wherein many oscillating or reciprocating parts are replaced by continuously rotating members.